AEROSIL and AEROXIDE fumed metal oxides for powder coatings. Technical Information 1340

Transcription

1 AEROSIL and fumed metal oxides for powder coatings Technical Information 1340

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3 Table of contents 1 Introduction Page 4 2 Technical Fundamentals of AEROSIL and for Powder Coatings 4 3 New Investigations on AEROSIL and in Powder Coatings Test Methods Flowability Angle of Repose Bed Expansion Transfer Efficiency Faraday Cage Effect Gloss Gel Time AEROSIL and Products in Polyester based Powder Coatings (Corona Application) Flowability Angle of Repose Test Bed Expansion Test Transfer Efficiency Faraday Cage Effect Gloss Gel Time Products in Polyester based Powder Coatings (Tribo Application) Transfer Efficiency Faraday Cage Effect Physico-Chemical Data and Registration of AEROSIL and 14 8 Conclusion 15 3

4 1 Introduction 2 Technical Fundamentals of AEROSIL and for Powder Coatings The global market for powder coatings is expected to grow at rates higher than liquid coatings due to the ongoing shift from conventional solvent-borne to more environmentally-friendly coating systems. The overall growth rate is estimated to be in the range of 5 6 % in the years ahead. While North America and Western Europe should see a more moderate growth, an above average increase in powder coatings production and consumption is expected for South-East-Asia, China, India and Eastern Europe. In order to remain competitive, it will be essential for powder coating manufacturers to develop innovative solutions and systems offering superior performance. Differentiation from the competition can be achieved by demonstrating properties such as free flow, transfer efficiency and edge covering. AEROSIL fumed silica and fumed oxides are well known for enhancing and optimizing manufacturing, quality, appearance and overall performance of powder coatings. A recent study performed between the Evonik Industries AG and the University of Western Ontario, Canada, shows the performance of newly developed fumed oxides in comparison to the established product range of AEROSIL fumed silica and fumed oxides. All tests were conducted in a polyester based coarse powder coating in comparison to a fine powder coating system and we will present the findings beginning in Chapter 3. AEROSIL fumed silica is an amorphous silicon dioxide with an extremely small primary particle size. Hydrolysis of chlorosilanes in an oxygen-hydrogen flame produces this fluffy white powder of high purity. Primary particles in the range of 7 to 40 nm result, in a wide range of specific surface areas, from 380 down to 50 m 2 /g. By using the AEROSIL process, other special oxides (brand name ) such as fumed aluminium oxide, titanium dioxide or zirconium oxide have been developed. AEROSIL and Improve free flow characteristics Enhance storage stability Reduce moisture pick-up Improve edge covering Alu C increases the electropositive chargeability of tribo powders To considerably improve free flow properties, 0.1 to 0.3 % by weight (on total) of AEROSIL fumed oxides should be added to the powder coating. When incorporating AEROSIL fumed oxides by suitable feeders before the final milling step, high homogeneous distribution results throughout the powder coating can be achieved. Another common incorporation method is the addition of AEROSIL fumed oxides at the end of the milling process by dry blending (after classification). Using this approach, there is a possibility that larger agglomerates may remain. Finally, the manufacturer has the option to adjust the incorporation to suit their specific processes and performance requirements. 4

5 The electrostatic charge of the powder coating will not be adversely affected, regardless of whether the powder has a positive or negative charge. The use of hydrophobic AEROSIL grades will ensure a long-lasting and consistent chargeability due to its moisture protection. The generally very low added amounts of < 0.5 % do not negatively influence the levelling of the powder coatings during curing. Alu C, which is produced using the same process as the AEROSIL fumed silica, has a special, dual performance enhancement status. Unlike most AEROSIL products, which have strong tendencies toward negative charges, Alu C has a strong tendency to a positive charge. For this reason, this product is often used in powder coatings that are triboelectrically applied, both to increase the electropositive charge of the powder coating during application to enhance the deposition or transfer efficiency and also to reduce static charge build-up in the final powder coating which can negatively influence bulk flow properties. Table 1 General overview of the use of AEROSIL and fumed Powder Coatings Systems Products Concentration in wt % Effect Thermosettings Powders Low molecular weight epoxy TGIC-polyester Epoxy polyester hybrids Polyurethanes Acrylics AEROSIL 200, AEROSIL 380, AEROSIL R 972, AEROSIL R 812, AEROSIL R 8200 Alu C, Alu C Free flow additive - Anti-caking (prevention of moisture pick-up) Thermoplastic Powders Vinyl Nylon Polyolefin Fluorcarbon types AEROSIL R 972, AEROSIL R 812, AEROSIL R 8200 Alu C, Alu C Free flow additive - Anti-caking (prevention of moisture pick-up) Tribopowders Epoxy polyester hybrids Epoxy acrylate hybrids Alu C, Alu Free flow additive - Increase in electropositive charge (tribo) AEROSIL 200 and AEROSIL 380 are hydrophilic fumed silicas which can be added into the hopper at % by weight (based on total) to improve blending of powders giving a more homogeneous dry mix ready to be fed into the extruder. Processing rheology is improved which allows for faster throughput and less hang-up in the extruder. AEROSIL R 972 is a hydrophobic fumed silica which can be added into the hopper at % by weight (based on total) to improve blending and give a more homogeneous dry mix. Excessive static charge build-up of powdered raw materials in the hopper causes fine particle size components to cling to the walls preventing a homogeneous blend and the feeding of material into the extruder. AEROSIL R 972 can also be added at % by weight (based on total) before pulverization and ground with the powder to reduce static charge, improve flow of the final product and flow during deposition. AEROSIL R 972 imparts a slight hydrophobic character to the powder preventing moisture pick-up during storage which can cause caking. AEROSIL R 972 can be dry blended after pulverization if it is not possible to add prior due to being separated out in the classifiers. The loading levels of AEROSIL R 972 are within the same range whether added before or after pulverization, however, before pulverization gives the optimum results. 5

6 AEROSIL R 812 and AEROSIL R 8200 are HMDS treated fumed silicas which are characterized by their strong hydrophobicity. The very hydrophobic nature of these grades provides an excellent moisture protection and an elevated chargeability. Alu C is a positively charged fumed aluminium oxide which can be added before pulverization or dry blended as an after treatment for all types of powder coatings. Due to the positive charge, it is extremely suited for tribo applications and in some cases Alu C makes non-tribo chargeable powders tribo-chargeable. Alu C and Alu 130 are included to reduce static charge which reduces flow and assists the deposition of the powder during application. Recommended loading levels are between % by weight (based on total). The benefits of Alu C and Alu 130 are due in part to the fine particle size and distribution from our manufacturing process and the surface charge of the particle itself. Alu C 805 is an Octylsilane treated fumed aluminium oxide. By adding % by weight (on total) it improves the flowability of all types of powder coatings. Due to its hydrophobic character Alu C 805 reduces moisture pick-up and enhances storage stability. AEROSIL Fumed Silica improves free flow characteristics right: Powder coating without AEROSIL fumed silica left: Powder coating with AEROSIL R 972 6

7 3 New Investigations on AEROSIL and in Powder Coatings This Technical Information brochure provides information regarding a recent study of performance properties including flow behavior, which can be influenced by fumed silica or aluminium oxides in a customary powder coating. Increasing environmental concerns, combined with the need to contain costs and achieve improved appearance properties have accelerated the trend toward development of thinner powder coating films. This is being achieved through the use of smaller particle size powder coatings and as a consequence opens the door to using different additives to optimize performance. To meet the existing and future requirements of powder coatings, two different particle sizes were included in the study and a variety of performance properties were tested. Specific attention was paid to ultra fine powders, as good flow and spray characteristics are known to be a challenge to achieve. The main objective of the study was to evaluate the effectiveness of different fumed silicas and aluminium oxides on the performance of powder coatings. All tests have been made in a black polyester based formulation. To get a comprehensive overview about the performance in powder coatings of different fineness, two particle sizes were chosen (fine powder: d 50 = 21.5 µm / coarse powder: d 50 = 31.0 µm). The additive concentration was set 0.5 % by weight (based on total) for the fine and 0.3 % by weight (based on total) for the coarse powder coating. For both fine and coarse particles the additives were incorporated into the powder coating with AMC milling equipment using proprietary technology of the University of Western Ontario, Canada. As a general rule, slightly higher loading levels of additive are needed to adequately cover smaller particle size powders. This is the background of the difference in loading levels, based on powder particle size. Table 2 Evaluated fumed silica and aluminium oxides Product Character BET Surface [m²/g] Tapped Density [g/l] Surface Chargez AEROSIL 200 Hydrophilic Silica 200 ± Negative AEROSIL R 812 Hydrophobic Silica 260 ± Negative AEROSIL R 972 Hydrophobic Silica 110 ± Negative Alu C Hydrophilic Aluminium Oxide 100 ± Positive Alu C 805 Hydrophobic Aluminium Oxide 100 ± Slightly Positive Alu 130 Hydrophilic wwaluminium Oxide 130 ± Positive While use of hydrophilic and hydrophobic fumed silica (AEROSIL ), and hydrophilic aluminium oxide () are well known in the powder coatings industry, Evonik has developed new fumed oxides, which enhance the properties of powders. In cooperation with the University of Western Ontario, Canada, these new particles were tested in comparison to the established product portfolio offered by Evonik for many years. This Technical Information gives an overview about the performance of fumed oxides in a polyester based powder coating including both, coarse and fine powders. All products included in this study are listed in Table 2 with their respective physical properties. The following tests have been performed with the polyester powder coatings: Angle of Repose (Flowability) Bed Expansion (Flowability) Powder Transfer Efficiency Faraday Cage Effect Gloss Gel Time 7

8 4 Test Methods 4.1 Flo wability Angle of Repose Angle of repose (AOR) is a commonly used parameter in determining the flowability of a powder. It is defined as the angle between the surface of the pile (formed by raining down the powder to a flat surface) and the flat surface. A lower angle of repose indicates a better flowability. 4.2 Transfer Efficiency Transfer Efficiency tests were carried out with a GEMA manual spray gzzun and an aluminium target panel of 30 cm in diameter and 20 cm away from the gun. Each powder sample was tested three times with an initial powder mass of 3 grams each and the average transfer efficiency (E) was calculated from these three results (E 1, E 2 and E 3 ): Bed Expansion Bed expansion ratio (BER) is another commonly used parameter in determining the flowability of a powder. BER is defined as the ratio of fluidized bed height H over the initial fixed bed height H 0, which changes with the air velocity passing through the bed. A higher expansion ratio suggests improved powder performance, fluidization ability and flowability. E 1 + E 2 + E 3 Transfer Efficiency E = = m 1 + m m where m 1, m 2 and m 3 were the powder mass transferred to the target panel. 4.3 Faraday Cage Effect Faraday Cage Effect tests were conducted with a specially designed aluminium panel of 7 x 6 with a 1 deep x 1 wide trough located in the centre, as shown in the the picture below. Three strips of aluminium sheets (1 x 6 ) were attached to their corresponding positions (2 on the outside of the trough and 1 on the back wall inside the trough by small clips before spraying. Aluminium panel and 3 strips of aluminum sheets designed for the Faraday Cage Effect test Aluminium sheets Aluminium panels and fixed strips after spraying Acrylic column used for the bed expansion tests 8

9 5 AEROSIL and Products in Polyester based Powder Coatings (Corona application) Then the whole panel was hung in the spray booth with grounding connection. Each of the 3 strips was weighed before and after each spray to get the mass of powder deposited. By comparing the powder mass on the back wall inside the trough (m internal ) with the average powder mass on the 2 strips outside of the trough (m outer ) with m outer = m outer (top) R = + 2 m internal m outer m outer (bottom) the Faraday Cage Effect can be determined by the ratio of these two mass numbers: with R = 1 denoting no Faraday Cage Effect and R = 0 representing a maximum Faraday Cage Effect and no powder transferred to the internal surface. 4.4 Gloss The evaluation of the gloss values for the different samples of coarse and fine polyester powder was performed with the Novo-Gloss Gloss meter manufactured by Rohpoint Instrumentation Ltd. According to the manufacturer, the assigned value has an uncertainty value of 0.5 units at 95 % confidence level. The selected angles of the incident light to carry on the test are 20 and 60, these values are widely used in industry as a standard for gloss measurements. Each individual panel was measured six times at different points to calculate the average gloss value., All samples for the tests of fumed silica and fumed aluminium oxides were prepared as described in chapter 3. The procedure for fluidization tests, transfer efficiency, Faraday Cage Effect, gloss and gel time were done according to chapter Flowability Angle of Repose Test In coarse as well as in fine polyester powder coatings, Alu C 805 showed the highest positive impact on the flow characteristics among the tested fumed aluminium oxides. The second best performing product was Alu 130 for both particle sizes (Figure 1 and 2). Angle of Repose* Figure Angle of Repose of aluminium oxides in a coarse powder coating Alu C Alu C 805 * A low angle of repose indicates improved flow behaviour Figure 2 Angle of Repose of aluminium oxides in a fine powder coating Alu Gel Time The ASTM standard test method (D ) for gel time of a thermosetting powder coating was used for this experiment. This test method determines the amount of time required for a thermosetting coating powder to gel on a metal surface at a specified temperature. An equal mass of each sample was placed on a heated surface at 200 C with a variance of +/- 2 C. The time between initial heating and the onset of hardening, is defined as the gel time. Angle of Repose* Alu C Alu C 805 * A low angle of repose indicates improved flow behaviour Alu 130 9

10 Regarding the use of fumed silica in the polyester based test material, AEROSIL R 812 and AEROSIL 200 enhanced the flow properties to a higher extent compared to all other tested silica products (Figure 3 and 4). This statement can be applied for the fine and coarse polyester powder coating. Angle of Repose* Figure Angle of Repose of silicas in a coarse powder coating AEROSIL AEROSIL R * A low angle of repose indicates improved flow behaviour AEROSIL R Bed Expansion Test In comparison to the angle of repose test, the bed expansion test is the more direct characterization method when evaluating the fluidization properties of a powder coating. In Figure 5 and 6, the results for all silica and aluminium oxides are given. The graphics show the air velocity U [cm/s], which is needed to obtain 20 % bed expansion. The air velocity of the control without silica or aluminium oxide was always > 1 cm/s. All tested silicas and aluminium oxides clearly improve the flowability of the polyester based powder coating in the bed expansion test. For the fine polyester powder, aluminium oxides are observed to be more effective compared to silica products with Alu C 805 and Alu C performing best. For the silica materials, the best result was obtained with the hydrophobic AEROSIL R 812. In the coarse powder coating, fumed silicas were observed to be slightly better as a fluidization additive. However results obtained with Alu C 805 and Alu 130 are very close in performance. Figure 4 Angle of Repose of silicas in a fine powder coating Figure 5 Bed Expansion test with silica and aluminium oxides in the fine powder coating Angle of Repose* AEROSIL AEROSIL R AEROSIL R 972 Air Velocity U [cm/s] Alu C 805 Alu C Alu 130 AEROSIL AEROSIL R AEROSIL R 972 Worse Better * A low angle of repose indicates improved flow behaviour Overall it can be stated that all tested additives improve the flow behaviour in the angle of repose test. Superior flow properties are provided by AEROSIL R 812, AEROSIL 200 and Alu C 805 in the coarse and fine polyester powder coating system. Air Velocity U [cm/s] Figure AEROSIL R 812 Bed Expansion test with silica and aluminium oxides in the coarse powder coating Alu C 805 Alu 130 AEROSIL AEROSIL 200 R 972 Alu C Worse Better 10

11 As a summary of the overall result: for coarse and fine polyester powder coatings Alu C 805 and AEROSIL R 812 are the products which provide the highest efficiency concerning positive impact on fluidization. Due to their hydrophobic nature, both materials, in addition to their excellent flow behaviour, prevent moisture pick up of the powder coating during storage and processing. It must be noted here that selection of the best additive to enhance fluidization performance is always formulation dependent. It is very possible that what works best in one system may not give the optimum results in all formulations. 5.2 Transfer Efficiency To evaluate the transfer efficiency with the corona process, a GEMA spray gun with a target panel of 30 cm diameter and 20 cm distance between panel and gun was used. 3 g of powder coating were sprayed to cover the disks. The higher the coverage of the disks after spraying, the more powder coating was transferred. The drying time was ten minutes at 200 C. It was evident that the results for the transfer efficiency are very much dependent on the particle size of the powder coating. Additives which enhanced the transfer efficiency for fine powders tended to reduce the transfer efficiency of the coarse powder coating. In fine powders AEROSIL 200 and AEROSIL R 812 performed best (Table 3) while in coarse powders Alu 130 and Alu C gave favourable results (Table 4). Table 3 Product AEROSIL 200 AEROSIL R 812 Alu C Transfer Efficiency [%] Table 4 Product Results of Transfer Efficiency in the fine powder coating Results of Transfer Efficiency in the coarse powder coating Alu 130 Alu C Alu C 805 Transfer Efficiency [%] Faraday Cage Effect For the tests of the Faraday Cage Effect the powder coatings were sprayed with the GEMA spray gun onto the panels. The final evaluation of the covering effect was evaluated as outlined in chapter 4.3. A maximum Faraday Cage Effect provides bad coverage and that corresponds to a low R value. R = 1 represents no Faraday Cage Effect and a uniform coverage over the entire substrate. In fine powder materials, silica additives help to overcome the Faraday Cage Effect and achieve a more uniform coverage of the substrate results show AEROSIL R 812 clearly improves this performance attribute. Figure 7 Influence of AEROSIL fumed silica on the Faraday Cage Effect in a fine powder coating. R = 1 denotes no Faraday Cage Effect (good substrate coverage) and R = 0 representing a maximum Faraday Cage Effect (bad substrate coverage) Better 0.69 R AEROSIL R 812 AEROSIL AEROSIL 200 R 972 Worse 11

12 6 Products in Polyester based Powder Coatings (Tribo Application) In coarse powder materials, only Alu C 805 improved the coverage slightly. All other tested silica and aluminium oxides did not provide noticeable benefits for the Faraday Cage Effect. 5.4 Gloss Gloss reductions were observed from the addition of each of the silica additives, for both incident angles (20 and 60 ) and for both coarse and fine powders. AEROSIL R 972 provided less influence on the gloss compared to all other tested fumed silicas. The test results indicate that generally silica additives have a greater impact to gloss than the aluminium oxide additi-ves. Excellent performance was demonstrated by Alu C 805, which did not influence the gloss of the powder coatings panels. In addition to the improvement of the flow properties, fumed aluminium oxide is often used to improve the chargeability of powders for the tribo application. For this reason, the influence of different aluminium oxide additives on the transfer efficiency and the Faraday Cage Effect was evaluated separately. 6.1 Transfer Efficiency The transfer efficiency was again performed as outlined in chapter 4.2. For the tests of different aluminium oxides a tribo application with a Nordson Tribomatic C manual spray gun was used. All tested aluminium oxides improved the transfer efficiency of the polyester material. While for the corona application the results are very much dependent on the particle size of the powder coating (see chapter 5.2), Alu C 805 showed a superior improvement of the transfer efficiency in the tribo application, independent of the powder coating particle size. 5.5 Gel Time For the gel times of coarse materials nearly no influence was observed with Alu 130 and Alu C 805 while AEROSIL R 812 and AEROSIL 200 tended to prolong the gel time. The same tendency was witnessed for the fine polyester powder coating, but due to the reduced particle sizes the onset of hardening was slightly faster compared to the coarse materials. Transfer Efficiency E [%] Figure Transfer Efficiency of aluminium oxides in the coarse polyester powder coating Alu C 805 Alu C Alu 130 Figure 9 Transfer Efficiency of aluminium oxides in the fine powder coating 80 Transfer Efficiency E [%] Alu C 805 Alu C Alu

13 6.2 Faraday Cage Effect The Faraday Cage Effect was tested according to the method described in chapter 4.3. For the spraying a Nordson Tribomatic C manual spray gun was used. A maximum Faraday Cage Effect provides a bad coverage and that means a low R value. R = 1 represents no Faraday Cage Effect and a consistent coverage all over the substrate. Figure 10 Faraday Cage Effect of the coarse powder coating with tribo application Better 0.6 R Alu C 805 Alu C Alu 130 Worse In the coarse powder coating, an improvement in covering the three-dimensional aluminium sheets was achieved with all tested aluminium oxides. Alu C 805 and Alu 130, in particular, showed a nice improvement of the powder penetration (Figure 10). In the fine powder coating only Alu 130 helped to overcome the Faraday Effect and to enhance the powder penetration in deeply recessed areas of the aluminium sheet. 13

14 7 Physico-Chemical Data and Registration of AEROSIL and Table 5 Physico-chemical data and registration of AEROSIL and AEROSIL Testmethod Unit R 972 R 812 R 8200 Alu 130 Alu C Alu C 805 Specific surface area (BET) m 2 /g 200 ± ± ± ± ± ± ± ± 15 Tapped density (approx. value ex plant) acc. to DIN EN ISO 787/XI, Aug g/l Moisture (ex plant) 2 hours at 105 C wt. % ph-value in 4 % dispersion * Carbon content wt. % SiO 2 -content based on ignited material wt. % Al 2 O 3 -content based on ignited material wt. % * Production in Rheinfelden The data have no binding force. EINECS (Europe) TSCA (USA) AICS (Australia) DSL (Canada) PICCS (Philippines) MITI (Japan) KECI (Korea) IECS (China) NZloC (New Zealand) AEROSIL 200 registered registered registered registered registered registered AEROSIL 380 registered registered registered registered registered registered AEROSIL R 972 registered registered registered registered registered registered AEROSIL R 812 registered registered registered registered registered registered AEROSIL R 8200 registered registered registered registered registered registered Alu C registered registered registered registered registered registered Alu C 805 registered registered registered registered registered Alu 130 registered registered registered registered registered registered The data have no binding force. 14

15 8 Conclusion The study of fumed silicas and fumed aluminium oxides in the polyester powder coatings has once again confirmed the positive effects that nano structured particles impart to powder coatings. While Alu C, AEROSIL 200, AEROSIL R 812 are well known for their excellent suitability in enhancing the desired properties of powder coatings, this study has shown that recent developments such as Alu C 805 and Alu 130 offer additional benefits in the tested systems. Consistent improvement was demonstrated in powder coatings treated with hydrophobic aluminium oxide Alu C 805, and it proved to be a very efficient additive to improve the flow behavior in fine and coarse powder coatings as well. Focusing on the tribo application, the Transfer Efficiency of Alu C 805 was superior in both fine and coarse powders while the Faraday Cage Effect was overcome especially in coarse materials. For the specific system used for this study it can be concluded that Alu C 805 and AEROSIL R 812 showed the best overall results and can therefore be considered the most suitable additives for both, coarse and fine particle size powders. Our most recent product developments will enable you to further improve the performance of your individual powder coating systems in order to compete in the growing powder coating market with highly innovative product solutions. We will be happy to assist you with our technical expertise to select the most suitable product for your specific system. 15

16 This information and any recommendations, technical or otherwise, are presented in good faith and believed to be correct as of the date prepared. Recipients of this information and recommendations must make their own determination as to its suitability for their purposes. In no event shall Evonik assume liability for damages or losses of any kind or nature that result from the use of or reliance upon this information and recommendations. EVONIK EXPRESSLY DISCLAIMS ANY REPRESENTATIONS AND WARRANTIES OF ANY KIND, WHETHER EXPRESS OR IMPLIED, AS TO THE ACCURACY, COMPLETENESS, NON-INFRINGEMENT, MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE (EVEN IF EVONIK IS AWARE OF SUCH PURPOSE) WITH RESPECT TO ANY INFORMATION AND RECOMMENDATIONS PROVIDED. Reference to any trade names used by other companies is neither a recommendation nor an endorsement of the corresponding product, and does not imply that similar products could not be used. Evonik reserves the right to make any changes to the information and/or recommendations at any time, without prior or subsequent notice. AEROSIL and are registered trademarks of Evonik Industries or its subsidiaries. Europe / Middle-East / Africa / Latin America Evonik Resource Efficiency GmbH Business Line Silica Rodenbacher Chaussee Hanau Germany phone fax ask-si@evonik.com North America Asia Pacific Evonik Corporation Business Line Silica 299 Jefferson Road Parsippany, NJ USA phone fax ask-si-nafta@evonik.com Evonik (SEA) Pte. Ltd. Business Line Silica 3 International Business Park #07-18, Nordic European Centre Singapore phone fax ask-si-asia@evonik.com TI JUL15